1. Field of the Invention
The present invention relates generally to road grading equipment and in particular to a drag-type road grader.
2. Description of the Prior Art
Nonpaved roads comprising dirt, gravel and the like generally require periodic maintenance to repair the damage done thereto by vehicular traffic. A common maintenance procedure is to regrade and relevel the roads with equipment especially designed for this purpose. For example, self-propelled road graders are well known and may be provided with blades for scraping, leveling and reshaping a road surface. The blades are generally adjustably mounted with respect to height, pitch and angle relative to the direction of travel. For road grading purposes, the blades are usually oriented at an oblique angle with respect to the direction of travel so that excess road material flows transversely.
However, such self-propelled, conventional road graders have several drawbacks for the maintenance of roads comprising dirt, gravel and the like. First of all, generally only a single blade is mounted thereon. The single blade performs both cutting and filling operations wherein material is respectively removed from the high spots and deposited in the low spots. The only packing and compression of such redistributed material which occurs is by the rear wheels of the vehicle. Therefore, only the fractional portion of the blade's swath directly in the path of the vehicle rear wheels is compacted.
Secondly, self-propelled road graders operate best on relatively dry roads because their blades tend to stick in damp road materials. However, dry, loose material is susceptible to being blown out of level before being compacted by vehicular traffic. For example, pot holes filled under dry conditions with a single-blade road grader may be emptied and reopened by a high wind.
Yet another disadvantage of conventional, self-propelled road graders is their slow operating speeds. Excessive blade vibration or "chatter" typically occurs at speeds of approximately four miles per hour. The relatively slow operating speeds of such equipment tend to increase the cost of road maintenance therewith through such factors as labor, equipment usage, fuel consumption, maintenance and the amount of equipment required to maintain a given road network.
Drag-type road graders are also well known and are pulled along roads by tractors and the like. In fact, such drag-type road graders may be successfully employed in combination with self-propelled, single-blade road graders since the addition of the former can help compensate for the deficiencies of the latter. An exemplary drag-type road grader is shown in the Hall U.S. Pat. No. 1,185,090 and comprises a rectangular frame with a pair of blades extending thereacross at oblique angles. The Thurston U.S. Pat. No. 1,303,415 shows a frame with transverse blades. The frame members of the Thurston device are pivotally connected whereby the frame may be skewed to form a parallelogram to adjust the angles of the blades with respect to the direction of travel.